Arc melting furnace



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fflynowo Z. Soar/veal! United States Patent 2,726,278 ARC MELTING FURNACE Raymond L. Southern, New Kensington, Pa., assignor to Titanium Metals Corporation of America, Pittsburgh, Pa., a corporation of Pennsylvania Application August 27, 1954, Serial No. 452,639

3 Claims. (Cl. 13--9) This invention relates to are furnaces and more particularly to the type of furnace in which a consumable electrode is employed.

Consumable electrode arc furnaces are often employed for melting refractory metals such as titanium, zirconium, and molybdenum. In general they comprise a crucible and mechanical means for graduallylowering the electrode as the melting action of the arc transfers metal into the crucible to form the ingot. Electrodes employed to produce heavy ingots are necessarily long and difiiculty has heretofore been encountered in charging electrodes into the furnace; therefore a tiltable top structure has often been employed. Such tilting structures however are mechanically weak and it has been difiicult to accurately align the electrode with respect to the melting crucible. In addition the tilting top and associated mechanism for lowering the electrode has of necessity been complicated to provide for accommodation and support of the electrode in both horizontal and vertical positions and has generally made direct electrical connection to the electrode impossible. Contact rollers or shoes have therefore been employed which have necessitated additional mechanical operation with accompanying loss of reliability.

It is the object of this invention to provide a simple, efiicient, and more conveniently operated arc furnace. Another object of this invention is to provide such a furnace in which the alignment of the electrode and crucible is substantially improved. Still another object of this invention is to provide such a furnace having improved means for supporting and lowering the electrode during melting. A further object is to provide such afurnace into which the electrode can be charged in a vertical position without tilting or radically. disassembling the furnace. An additional object of this invention is to provide such a furnace having more efficient and reliable means for providing electrical connections. These and other objects of this invention will be apparent from the following more complete description thereof-and from the annexed drawings in which:

Fig. 1 shows a general sectional front view of a furnace embodying features of this invention.

Fig. 2 shows a sectional side view of the furnace of Fig. 1.

Fig. 3 shows a sectional view of the furnace taken along the line 3-3.

Fig. 4 shows a sectional view of the electrode carrier.

Fig. 5 is an enlarged detail view illustrating the means employed to attach the crucible housing to the electrode housing.

Fig. 6 shows in more detail a side view of the. arrangement for charging the electrode into the furnace, and showing the furnace of Fig. 1 with the crucible holder disconnected from the electrode housing.

Fig. 7 shows a top view of the crucible and its housing in position separated from the furnace proper for discharging.

Referring particularly to Figs. 1, Z and 3, a furnace trode housing indicated generally at 10, and a detachable crucible housing indicated generally at 12. The electrode housing, due to the internal mechanism, may be formed of several sections, as for example in the embodiment shown, upper section 14, middle section 16, and throat section 18. It is suitably and rigidly supported as by vertical columns 20, and horizontal girders 22 and firmly maintained by angle braces 23. The bases of the columns 20, may be supported by horizontal I beams 24, which are securely anchored in foundation material. It is preferred that beams 24, span a pit or an opening to a lower floor, as illustrated, to provide working room for handling the electrode, the crucible and associated structures as hereinafter described in more detail.

The upper section 14, of the electrode housing 10, is provided with a load bearing top which may comprise heavy plate 26, suitably braced by vertical angle members 28. Passing through plate 26, is screw shaft 30, which is rotatably mounted and depends from thrust bearing 32. Suitable and conventional means for rotating shaft 30, may conveniently be located on the upper surface of plate 26, and comprise electric motor 34, which is connected to the upper projecting end of shaft 30, by means of angle reducing gear 36. The portion of the shaft 30, inside the housing 10, is threaded and transfixes nut 37. Attached to the top of nut 37 is block 38, with extending fingers 39, which engage threads in He shaft 30, to clean these of any impurities which might affect free screw thread action between shaft 30, and nut 37, which is fixedly attached to the top of hollow cy indrical electrode carrier 40. Carrier 40, is supported by screw shaft 30, and vertical movement thereof is controlled rotating the said shaft, the carrier 40, being fixed as regards rotational movement itself by engagement of continuous ribs 42, attached to opposite sides thereof, with interior angle guides 43, which form tracks in support members 28. The interior of electrode carrier 40, as is shown most clearly in Fig. 4, contains an interior copper 'pipe 44, into which the lower portion of shaft 36, is disposed. Surrounding pipe 44, is another concentric copper pipe 45, and the space between the outside of pipe 45, and the interior Wall of carrier 40, forms Water jacket 46. Water inlet pipe 48, communicates with the space between pipes 44, and 45, so that water may flow downwardly and then out through perforations 50, in the bottom of pipe 45, into the water jacket 46, and out through outlet pipe 52, to insure proper flow of cooling water through the jacket 46. Copper pipes 44, and 45 are arranged ingood electrical contact with copper plate 54, at the top of carrier 49, which in turn is connected with flexible looped cables 56, which lead out through the outer walls of the housing through conventional glands 58. Flexible water hoses 60, and 61, communicate with water inlet and outlet means 48, and 52, and may conveniently pass through: the same glands 58, to connect with appropriate water supply and disposal means which themselves form no part of this invention. Electrical connection to suitable power source may be made through extending terminals 62.

The bottom of electrode carrier 40, is provided with electrode attaching means which comprises copper plate 63, which is in electrical contact with central pipes 44, and 45, and which abuts and makes contact with the upper surface of an electrode 64. The electrode 64, is firmly maintained in position centrally aligned with respect to the crucible below and in good electrical contact with plate 63, by provision of encircling clamp members 66, which may be tightly clamped around the electrode by the action of bolts 68, and which are welded to straps 70, which are fixedly attached to the side walls of carrier 40, as by bolts '72. In the event that the furnace of this invention is employed for remelting ingots which have previously been first melted into solid state from powder or sponge form, the electrode holder more particularly described and claimed in my copending application Ser. No. 362,592, filed June 18, 1953, of which this application is a continuation-in-part, will be found to be particularly advantageous.

The crucible housing 12, is demountably attached to the open bottom of the throat section 18, of electrode housing 10. Inside crucible housing 12, is crucible 74, preferably of copper which is provided with extending flange 75, at its open top which rests on corresponding flange 76, at the top of the housing 12, and the two flanges are sealed water tight by provision of interposed gasket 77, preferably of rubber. The space between the outside of crucible 74, and the inside wall of housing 12, forms cooling jacket 78, which is supplied with cooling fluid, for example water, by provision of intake 79, and outlet 80. The top flange 75, of the crucible 74, mates with a corresponding extending flange 82, on the bottom of the throat section 13, of the electrode housing but is electrically insulated therefrom by interposition of insulating ring 84, which may be fabricated of a fibrous material impregnated with a suitable synthetic resin of high dielectric strength. Insulated bolts 86, passing through flanges 82, 75, and 76 maintain the crucible housing 12, with its contained crucible 74, in fixed but removable relationship to the bottom of the electrode housing during the melting operation. Power is supplied to the consumable electrode by connection 62, and to the crucible, which forms in effect the other electrode by provision of terminal 83, which is conveniently attached to or made a part of extending crucible flange 75.

When in melting position the crucible housing 12, is firmly attached underneath the electrode housing 10. To discharge a melted ingot the bolts 86, are loosened and the crucible housing with the crucible and ingot contained therein is lcwere as a unit onto a frame 90, which is in turn supported by trolleys 92, which ride on rails formed by the lower flange portions of support beams 24, which are disposed horizontally below and around said crucible housing and extend laterally outwardly therefrom. When in detached and lowered position the crucible housing will be supported on frame 90, by means of extending lugs 94, and may be rolled on the trolleys 92, out from underneath the furnace proper.

The driving motor 34, is preferably controlled by an electrical circuit which responds to changes in the arc current or voltage so that proper motion of the electrode carrier will result in substantially uniform melting of the electrode 6 3. Such electrical circuits and associated controls are well known in the electrical art, are commercially available and themselves form no part of this invention.

in operation of the furnace an electrode 64, which may have been previously formed by compacting crude metal or a mixture of metal and appropriate alloying elements, or may be a previously melted ingot which is to be remelted to obtain improved homogeneity, is firmly attached to the electrode carrier by insertion of its prepared top between clamp members 6-6, and with its upper face in good electrical contact with carrier bottom plate 63. The clamp bolts 68, are firmly tightened to maintain the electrod fixedly in position. The crucible 74, in place in its housing 12, is then charged with an initial small supply of metal or alloy placed at the bottom of the crucible, to serve as a starting charge for the arc. The housing with contained crucible is then transferred into position under the electrode housing with the insulating ring 84, in place and the bolts 86, are firmly tightened to maintain the units in fixed relationship. In order to protect the metal being melted from oxidation during the melting operation an inert gas atmosphere may be maintained inside the furnace. If desired the furnace interior may be evacuated by connection of suitable and conventional pumping means to pipe 96, which communicat-cs with the throat section of the electrode housing,

, upper pipe 98, being temporarily sealed off. After evacuation the furnace interior may be flooded with a non-contaminating or inert gas such as argon or helium and if desired during the melting a constant flow of such gas may be maintained through the furnace entering at pipe 96, and being exhausted through pipe 98. After cooling fluid has been started circulating in the crucible housing water jacket 78, and the electrode carrier jacket 46, current is applied to the electrode terminals 62, and the crucible terminal 88, preferably the crucible terminal being connected to the positive side of a direct current power supply (not shown) and the electrode terminals to the negative, to initiate and maintain the arc. The driving motor control circuit may be adjusted so that a constant arc voltage is maintained and the electrode carrier will move vertically in response thereto.

Under these conditions, since the length of the are is related to the voltage a more or less constant distance may be maintained between the bottom of the electrode and the molten pool of metal in the crucible and as the electrode becomes gradually consumed and transferred to the crucible, the electrode will move automatically to maintain desired melting conditions. When the electrode has been consumed to the point where proximity of the arc to the clamps and carrier apparatus makes further melting undesirable the current is shut off and preferably, the ingot is retained in the furnace under noncontaminating atmosphere until reasonably cool. Then the crucible housing is disconnected from the electrode housing and lowered onto the frame below and rolled on the frame trolleys from underneath the furnace. The crucible with its contained ingot may then be removed from the crucible housing and the residual electrode stub removed from its clamps on the electrode holder. Removal of the ingot from the crucible and replacement of the empty crucible in its housing makes the furnace ready for recharging and another melting cycle.

It will be understood that when the size and weight of the electrode melted, and also the crucible and the crucible holder, is great, mechanical means may be employed for handling these. Such means may comprise any, or combinations, of well known and commonly employed mechanical devices, as for instance, hoists or winches, applied as will be obvious to those skilled in the art.

The furnace of this invention is simple, efficient and conveniently operated. The screw means employed for controlling the movement of the electrode carrier provides positive support and ready control and at the same time provides accurate alignment of the electrode with respect to the crucible. In addition the screw control is compact and may be self contained within the electrode carrier and the absence of complicated and bulky mechanisms simplifies operation and maintenance. With such an arrangement flexible power cable connections may be employed which eliminate the necessity for sliding shoes or rolling contact members and considerably improve the electrical reliability of the device.

I claim:

1. In an enclosed furnace for use in melting a consumable electrode into a crucible the combination comprising, a vertically mounted electrode housing, a crucible housing removably attached to the bottom of said electrode housing, an elongated hollow electrode carrier within said electrode housing, a nut fixedly attached ceno trally at the top of said electrode carrier, a screw shaft rotatably mounted and depending from the top of said electrode housing interiorly thereof and transfixing said nut with its lower end disposed interiorly of said electrode carrier and guide means cooperating with said electrode carrier to prevent rotation thereof during rotation of said screw shaft to control vertical movement of said electrode carrier during melting of an electrode held thereby into a crucible disposed in said crucible housing.

2. In an enclosed furnace for use in melting a consumable electrode into a crucible the combination comprising; a vertically mounted electrode housing, a crucible housing removably attached to the bottom of said electrode housing, an elongated electrode carrier Within said electrode housing, a longitudinal pipe within said electrode carrier, a nut fixedly attached at the top of said electrode carrier and over said pipe, a screw shaft rotatably mounted and depending from the top of said electrode housing interiorly thereof and transfixing said nut with its lower end disposed interiorly of said pipe, cooling means between the outer wall of said pipe and the inside wall of said electrode carrier and guide means cooperating with said electrode carrier to prevent rotation thereof during rotation of said screw shaft to control vertical movement of said electrode carrier during melting of an electrode held thereby into a crucible disposed in said crucible housing.

3. In an enclosed furnace for use in melting a consumable electrode into a crucible the combination comprising; a vertically mounted electrode housing, a crucible housing removably attached to the bottom of said electrode housing, an elongated electrode carrier within said 20 electrode housing, a longitudinal pipe within said electrode carrier of electrically conductive material ,and adapted to carrying electric current from the top to the bottom of said electrode carrier, flexible electrical connector means from the top of said electrode carrier connected to the top of said pipe and leading exteriorly of said electrode housing, electrode attaching means at the bottom of said electrode carrier, including means for maintaining an electrical connection between an electrode and the bottom of said pipe, a nut fixedly attached at the top of said electrode carrier and over said pipe, a screw shaft rotatably mounted and depending from the top of said electrode housing interiorly thereof and transfixing said nut with its lower end disposed interiorly of said pipe, cooling means between the outer wall of said pipe and the inside wall of said electrode carrier and guide means cooperating with said electrode carrier to prevent rotation thereof during rotation of said screw shaft to control vertical movement of said electrode carrier during melting of an electrode held thereby into a crucible disposed in said crucible housing.

References Cited in the file of this patent UNITED STATES PATENTS 721,703 Heroult Mar. 3, 1903 1,785,406 Cornett Dec. 16, 1930 2,686,825 Southern Aug. 17, 1954 FOREIGN PATENTS 3,503 Great Britain of 1893 

1. IN AN ENCLOSED FURNACE FOR USE IN MELTING A CONSUMABLE ELECTRODE INTO A CRUCIBLE THE COMBINATION COMPRISING, A VERTICALLY MOUNTED ELECTRODE HOUSING, A CRUCIBLE HOUSING REMOVABLY ATTACHED TO THE BOTTOM OF SAID ELECTRODE HOUSING, AN ENLONGATED HOLLOW ELECTRODE CARRIER WITHIN SAID ELECTRODE HOUSING, A NUT FIXEDLY ATTACHED CENTRALLY AT THE TOP OF SAID ELECTRODE CARRIER, A SCREW SHAFT ROTATABLY MOUNTED AND DEPENDING FROM THE TOP OF SAID ELECTRODE HOUSING INTERIORLY THEREOF AND TRANSFIXING SAID NUT WITH ITS LOWER END DISPOSED INTERIORLY OF SAID ELECTRODE CARRIER AND GUIDE MEANS COOPERATING WITH SAID ELECTRODE CARRIER TO PREVENT ROTATION THEREOF DURING ROTATION OF SAID SCREW SHAFT TO CONTROL VERTICAL MOVEMENT OF SAID ELECTRODE CARRIER DURING MELTING OF AN ELECTRODE HELD THEREBY INTO A CRUCIBLE DISPOSED IN SAID CRUCIBLE HOUSING. 